This invention relates to compositions, methods and kits for determining the presence and/or amount of vitamin D including vitamin D analogs and metabolites thereof in a sample suspected of containing the same.
The term “vitamin D” refers to a group of fat-soluble secosteroids. In humans, vitamin D is unique because it can be ingested as cholecalciferol (vitamin D3) or ergocalciferol (vitamin D2) and because the body can also synthesize it (from cholesterol) when sun exposure is adequate. Because of this latter property, vitamin D is considered by some to be a non-essential dietary vitamin although most consider it an essential nutrient. Vitamin D has an important physiological role in the positive regulation of calcium ion homeostasis. Vitamin D3 is the form of the vitamin synthesized by animals. It is also a common supplement added to milk products and certain food products as is vitamin D2.
Both dietary and intrinsically synthesized vitamin D3 must undergo metabolic activation to generate bioactive metabolites. In humans, the initial step of vitamin D3 activation occurs primarily in the liver and involves hydroxylation to form the intermediate metabolite 25-hydroxycholecalciferol (also referred to as calcidiol, calcifediol, 25-hydroxycholecalciferol, or 25-hydroxyvitamin D (abbreviated 25(OH)D). The latter compound, i.e., 25-hydroxyvitamin D, is the specific vitamin D metabolite that is measured in serum to determine vitamin D status. Calcidiol is the major form of Vitamin D3 in the circulatory system. Circulating calcidiol is converted by the kidney to 1,25-dihydroxyvitamin D3 (calcitriol; 1,25(OH)2D3), which is believed to be the most biologically active form of vitamin D.
Assessing vitamin D levels in biological samples is important since vitamin D deficiency is related to a number of disorders in mammals. There is a need for reagents and methods for accurate and sensitive determinations of concentrations of vitamin D, vitamin D analogs and metabolites thereof in samples.